FEEDING

I am new to Lugers. I have one that I bought many years ago( more than ten ) from J& G sales. It has been sitting around all of that time. Now that I am intrested in shooting it I am having trouble. I have four magazines for this pistol, two came with it and two are from GPC. I have not been able to get reliable feeding from any of them. I think the gun is intermittently short stroking. That is to say the breach block is not quite traveling back far enough to properly pick up the next cartridge. what I wind up with is the block riding over the cartridge base and the caridge tilted up at a high angle with the whole thing locked up. I am using some 124 grain bulleted ammunition from 3-D cartrige company, but do not know the powder charge or MV. Any suggestions? Can anyone suggest a good luger specialist if I send it out to get it working?

All help appreciated.